There is significant interest in the ability to use cells for a wide variety of therapeutic purposes. The hematopoietic system exemplifies the extraordinary range of cells involved in protection of mammalian hosts from pathogens, toxins, neoplastic cells, and other diseases. The hematopoietic system is believed to evolve from a single stem cell, from which all the lineages of the hematopoietic system derive. The particular manner in which the stem cell proliferates and differentiates to become determined in its lineage is not completely understood, nor are the factors defined. However, once the stem cell has become dedicated to a particular lineage, there appear to be a number of factors, for example colony stimulating factors, which allow, and may direct the stem cell to a particular mature cell lineage.
There are many uses for blood cells. Platelets find use in protection against hemorrhaging, as well as a source of platelet derived growth factor. Red blood cells can find use in transfusions to support the transport of oxygen. Specific lymphocytes may find application in the treatment of various diseases, where the lymphocyte is specifically sensitized to an epitope of an antigen. Stem cells may be used for genetic therapy as well as for rescue from high dose cancer chemotherapy. These and many other purposes may be contemplated.
In order to provide these cells, it will be necessary to provide a means, whereby cells can be grown in culture and result in the desired mature cell, either prior to or after administration to a mammalian host. The hematopoietic cells are known to grow and mature to varying degrees in bone, as part of the bone marrow. It therefore becomes of interest to recreate a system which provides substantially the same environment as is encountered in the bone marrow, as well as being able to direct these cells which are grown in culture to a specific lineage.